The reason people use Facebook is to share photos. But Facebook's photo-sharing experience on the mobile has been horrible for some time now.

It takes 6 slow-loading screens to upload a photo through the Facebook iPhone app. With Instagram there is one screen.

This created a huge opening for an attack on Facebook, and several startups have seized the moment, including Path, PicPlz, and Instagram.

In the absense of a good offering from Facebook, users flocked to these services, especially Instagram. It grew from 1 million users in January 2011 to 15 million in December 2011. It has 30 million users now.

According to Mary Meeker, sometime in the middle of 2013, there will be more people on the Internet via their mobile devices than desktops.